The invention is directed to a process and apparatus for recovering metals from dilute solutions. Particularly, it is desired to recover nickel and other metals from drag-out or rinse solutions (hereinafter referred to collectively as rinse solutions) leaving electroplating equipment.
Electroplating systems generate waste water streams containing significant concentrations of the metal being plated. Concentration of the metal in the waste stream may be in the range of a trace amount up to 2,000 ppm or higher.
The Environmental Protection Agency (EPA) has set stringent discharge limits on the concentration of various metals in waste streams. Various methods have been suggested for meeting these discharge limits (e.g., precipitation, electrolytic recovery, evaporation, reverse osmosis and ion exchange).
All of the suggested processes have drawbacks. For example, the precipitation method, which generally uses lime or alkali treating agents, produces a metal containing sludge which must be disposed of. This creates a landfill problem. With respect to the electrolytic and evaporation methods, both are energy intensive resulting in high operating costs since the waste streams being treated are typically quite dilute. Reverse osmosis has also been suggested. However, this process depends on delicate membranes which are sensitive to variations in pH and temperature. Additionally, the reverse osmosis process generates a concentrated waste that presents a disposal problem. Finally, ion exchange has enjoyed some degree of success because it is especially suited for dilute waste streams. However, the ion exchange process is a tedious operation and also generates a metal containing waste consisting of regeneration chemicals, back washes and rinses.
Accordingly, it is an object of the present invention to provide an effective yet economical process and apparatus for removing metals from dilute solutions, especially electroplating and electroless plating rinse solutions.
Additionally, it is an object of the present invention to provide a process and apparatus designed for retrofit in existing electroplating systems for recovering metals from the rinse solutions generated by the electroplating systems.
More particularly, it is an object of the present invention to provide a closed-loop process and apparatus suitable for new installations or retrofits for recovering metals from an electroplating bath rinse solution for reuse in the electroplating system while essentially generating no liquid or solid wastes requiring disposal.